1. Field of the Invention
The present invention relates generally to electronic devices, and more particularly to a battery charging and/or DC power supply circuitry.
2. Description of the Related Art
A conventional battery charger normally employs a high-cost, huge, and heavy transformer for stepping down the alternate current (AC) line voltage to get charging current for charging the battery. However, such battery charger is too heavy to be conveniently portable due to the heavy transformer.
A transformerless pulse battery charging circuitry was developed to eliminate the drawback of the aforementioned conventional battery charger. As shown in FIG. 7, a conventional pulse battery charging circuitry primarily employs a control circuit to intercept the low voltage from a negative-slope side of the AC power and the employs the low voltage as a charging power source to charge the battery. However, since the silicon controlled rectifier (SCR) fails to be turned off by the gate terminal once triggered, while encountering the condition of unstable AC power, like power phase deviation is occurred in the power supply of the power plant, or the power plug is in imperfect contact with the socket, the voltage level of the AC power tends to rise immediately before it drops to the cutoff level of the SCR to cause excessively heavy current to further burn the circuitry because the SCR fails to be turned off in time.
Further, the conventional direct current (DC) charging technology tends to crystallize the battery plate over a long time. After the crystallization, the reaction area of the plate is decreased and the output/input impedance is increased to further incur the aging of the battery. The aged battery tends to generate a virtual voltage while being charged to cause its undercharge, thereby incurring the short life of the battery.